Abstract: Long records of the latitude and speed of the North Atlantic eddy-driven jet stream since 1871 are presented from the newly available Twentieth Century reanalysis. These jet variations underlie the variability associated with patterns such as the North Atlantic Oscillation (NAO) and have considerable societal impact through variations in the prevailing westerly winds. While the NAO combines variations in the latitude and speed of the jet, these two characteristics are shown to have quite different seasonal cycles and interannual variability, suggesting that they may have different dynamical influences.

In general, the features exhibited in shorter records are shown to be robust, for example the strong skewness of the NAO distribution. Related to this is a clear multimodality of the jet latitude distribution which suggests the existence of preferred positions of the jet. Decadal variations in jet latitude are shown to correspond to changes in the occurrence of these preferred positions. However, it is the speed rather than the latitude of the jet which exhibits the strongest decadal variability, and in most seasons this is clearly distinct from a white noise representation of the seasonal means. When viewed in this longer term context the variations of recent decades do not appear unusual, and recent values of jet latitude and speed are not unprecedented in the historical record.

Umm, outside of Wasaburo Oishi in Japan in 1920, nobody knew there was a jet stream. When the Americans were dropping bombs in Japan, they couldn't work out why they kept missing the target. When the pilots calculated their airspeed, their bosses back at base didn't believe them. Not sure how anyone would be actively measuring the speed the of jet stream outside of Japan till the mid 1940s.